U.S. officials had said Saturday that the released prisoners would be taken to a U.S. military hospital in Landstuhl, Germany, for medical treatment. The hospital is near the U.S. military's Ramstein Air Base.

The said Washington Post reporter Jason Rezaian, former U.S. Marine Amir Hekmati, and pastor Saeed Abedini were on the flight, but a fourth freed American, Nosratollah Khosravi-Roodsari, was not.

A fifth American, student Matthew Trevithick was released independently of the larger swap, and already had headed home.

Meanwhile, the United States has imposed sanctions against 11 individuals and entities involved in Iran's ballistic missile program as a result of Tehran's firing of a medium-range ballistic missile.

U.N. experts said in a report in December that the missile test in October violated sanctions banning Iran from launches capable of delivering nuclear weapons.

A U.S. Treasury official says Iran's ballistic missile program poses "a significant threat to regional and global security."

The U.S. also believes there was a November missile test.

U.S. officials have said the Treasury planned to announce the penalties in late December, but held off after Iran's foreign minister said they could have derailed the prisoner exchange that took place this weekend.

The U.S. has just ended economic sanctions over Iran's nuclear program.